Wick flow is caused by the movement of buffer into the support medium. Moisture evaporation from the gel from heat generation during electrophoresis causes movement of the buffer into the gel. Gel absorption of buffer to replace the lost moisture affects the migration of sample molecules.
Using a lid or cover during electrophoresis can prevent some of this evaporation. Methods that generate excessive heat utilize a cooling system during electrophoresis to prevent wick flow and other damage to sample solutes.